Pipe-inclosed underground cable



D. BROOKS.

Pipe Inlosed Undergrouhd Gable.

PETERS, PHOTO-LITHOGRAPHER. WASHINGTON D C UNITED STATES PATENT OEErcE;

DAVID BROOKS, OF PHILADELPHIA, PENNSYLVANIA.

PIPE-INCLOSED UNDERGROUND CABLE.

SPECIFICATION forming part of Letters Patent No. 234,748, dated November 23, 1880,

Application filed February 16, 1880.

T 0 all whom it may concern Be it known that I, DAVID BROOKS, a citizen of the United States, and resident of Philadelphia, Pennsylvania, have invented certain Improvements in Metallic Pipes forElectrical Conductors Insulated in Oil, of which the following is a specification.

My invention relates to certain improvements in the system of underground telegraph-lines for which I have obtained Letters Patent of the United States, and in which a number of clothed electrical conductors are inclosed in metal pipes containing oil, which acts as an insulator, the object of my invention being to prevent the reduction of the insulatin g qualities of the oil.

I have discovered that the oxide of iron in the metal pipes or vessels is soluble in oil and mixes therewith, and consequently reduces or impairs the insulating properties of oil. To overcome this difficulty I coat the inner surface of the pipe with a solution of shellac, or shellac varnish, or similar varnish which will adhere closely to the metal surface and will not affect or be affected by the oil. The varnish which I have found most effective for the purpose is formed by an ordinary solution of shellac in alcohol, the proportions not varying essentially from the proportions of the ingredients in what is known as shellac varnish. After the liquid solution has been applied to the pipe all traces of alcohol should be removed by evaporation. For this purpose I first plug up one end of the pipe, as illustrated in Fig. 2, fill the latter with varnish, and then pour it 01f again, when a sufficient coating of shellac will be found adhering to the entire inner surface of the pipe, as illustrated in the sectional view, Fig. 1. To get rid of all traces of alcohol in this coating, which would be injurious to the insulating qualities of the oil, I pass through the coated pipe a current of hot air, which causes the evaporation ot' the alcohol. The pipe is then ready for the reception of the clothed telegra 'lhic conductors, which are usually introduced in the form of a cable in lengths, and the sections of piping and wire are joined together, and oil is then supplied to the pipes to insulate the electrical conductors.

I claim as my invention A telegraph-line consisting of a metallic pipe coated on its inner surface with shellac varnish and containing electrical conductors insulated in oil, substantially as described.

In testimony whereofIhave signed my name to this specification in the presence ot'two subscribingxwituessesi DAVID BROOKS.

Wmlesses ,PAMES F. TOBIN, [HARRY SMITH. 

